Geothermal energy collection system

ABSTRACT

This invention provides a method of extracting geothermal energy, generally comprising the steps of: insertion of a thermal mass into a Heat Absorption Zone, absorbing heat in thermal mass, raising the thermal mass to a Heat Transfer Zone, and transferring the heat from the thermal mass. The acquired heat can be used to generate electricity or to drive an industrial process. 
     The thermal mass can have internal chambers containing a liquid such as molten salt, and can also have structures facilitating heat exchange using a thermal exchange fluid, such as a gas or a glycol-based fluid. 
     In some embodiments, two thermal masses are used as counterweights, reducing the energy consumed in bringing the heat in the thermal masses to the surface. In other embodiments, solid or molten salt can be directly supplied to a well shaft to acquire geothermal heat and returned to the surface in a closed loop system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 61/633,756, filed on Feb. 17, 2012, the contents ofwhich are also incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of geothermal energy extraction, andmore specifically to the process of extracting heat from wells drilledinto the Earth and using the extracted heat for an industrial process,such as the generation of electricity, or to drive a chemical or othermanufacturing process.

BACKGROUND OF THE INVENTION

Mankind has used geothermal energy for millennia. It is known that humantribes of the Neolithic Age bathed in natural hot springs, and theancient Chinese and Roman civilizations built facilities to harnessgeothermal pools. With the core of the Earth believed to be over 5,000°C., it has been estimated that there is enough heat stored from theoriginal formation of the Earth and generated by ongoing radioactivedecay to meet mankind's energy needs for any foreseeable future.

The usual problems encountered in attempting to utilize geothermalenergy have been practical ones of access, since the surface of theEarth is much cooler than the interior. The average geothermal gradientis about 25° C. for every kilometer of depth. This means that thetemperature at the bottom of a well 5 km deep can be expected to be at atemperature of 125° C. or more. Oil companies now routinely drill foroil at these depths, and the technology required to create holes of thismagnitude in the Earth is well known. (The deepest oil well at this timeis over 12 km deep.) Wells of this depth, however, can be veryexpensive, costing over $10M to drill.

However, near geological fault zones, fractures in the Earth's crustallow magma to come much closer to the surface. This gives rise tofamiliar geothermal landforms such as volcanoes, natural hot springs,and geysers. In the seismically active Long Valley Caldera ofCalifornia, magma at a temperature more than 700° C. is believed to lieat a depth of only 6 km. Alternatively, if lower temperatures can beutilized, a well dug to a depth less than 1 km in a geothermal zone canachieve temperatures over 100° C. A well 1 km deep often can cost muchless than $1M to drill.

Electricity generation from geothermal energy was first demonstrated inItaly in 1904, but it was only in the 1950s that the first commercialoperations began. The initial approach, such as that used at the Geysersfacilities in Sonoma and Lake Counties, California, relies on naturalsteam within the Earth. At the Geysers, wells about 1-2 km deeppenetrate the cap rock into a stratum containing magma-heated steam at atemperature of about 170° C. and a pressure of about 700 kPa (about 7atm). The naturally high-pressure steam pushes to the surface throughthe well, and is directed to drive turbines to generate electricity. Thewater at the end is discarded as wastewater. (For more, see<http://www.geysers.com/>.)

A more ambitious multi-year project in Iceland, the Iceland DeepDrilling Project (IDDP) along the mid-Atlantic ridge plans to drillwells 5 km deep to tap into a source of 500° C. hot supercriticalhydrous fluid at about 220 atm in pressure. (For more, see<http://iddp.is/about/>.)

Both of these projects tap into naturally existing geothermal pools ofsteam or superheated fluid. Such a system, often called a geothermalwell, has its advantages in that the steam is naturally under pressure,and is replenished from a reservoir of groundwater. However, thistechnique can only be used in locations where there is magma nearer thesurface to provide heat, where there is a steady supply of ground waterto become pressurized steam, and a solid cap rock to keep the steamconfined and under pressure. These conditions restrict the applicabilityof this method to relatively few geographic sites.

More recent methods to utilize geothermal energy in hot, dry rock arecalled enhanced geothermal systems, or EGS. [See “The Future ofGeothermal Energy: Impact of Enhanced Geothermal Systems (EGS) on theUnited States in the 20 Century”, MIT Report, 2006, available at<http://www1.eere.energy.gov/geothermal/egs_technology.html >.] In sucha system all that is needed is for a pool of geothermal heat to exist ata depth where wells can be economically produced. In an EGS setup, afirst well is drilled several kilometers deep and large volumes of waterinjected down into the hot rock. The water can be injected attemperatures that fracture the lower hot rock to make it more permeable.This process is called hydraulic fracturing, or “fracking”. The waterbeing pumped into the injection well is then heated below the surface tobecome steam, and pumped out in a second well. This method forgenerating electricity is therefore similar to the previously describedtraditional geothermal technique, except in EGS the water is supplied bythe system. The spent water, once the heat has been extracted togenerate electricity, is re-injected into the injection well.

FIG. 1 illustrates a prior art EGS system. At or near the surface of theEarth 10, an EGS facility 12 provides a pumping system that injectswater into the Earth and pumps water/steam from the Earth once heated.An injection well 14 extends into the Earth to a depth significantlyhotter than the surface 10. The region of the Earth at this hottertemperature is designated a thermal pool 560. Water is then injectedfrom the EGS facility 12 into the injection well 14, where it dispersesinto the thermal pool 560. Sometimes, the water is injected at suchpressures that it causes a network of fractures 570 in the hot rock ofthe thermal pool 560, making it more permeable to water, and increasingthe surface area of the rock in order to heat the water more quickly.Once the water is heated in the thermal pool 560, it is pumped out theproduction well 16, either as superheated water or as supercriticalsteam. The heated water/steam is used to drive a production facility 20to generate electricity.

EGS can be used anywhere there is a suitable stratum of hot rock ataccessible depths, as long as there is a supply of water to initiate theprocess and to replenish what is lost. Because the water/steam broughtto the surface is intended to be recaptured once the heat is extractedand re-injected into the injection well, this is called a closed loopsystem. It is proving a popular alternative for geothermal energy,notably because it can be used in far more geographic sites thantraditional geothermal wells.

EGS geothermal energy production facilities are being developed byseveral companies, including AltaRock Energy, Inc. of Seattle, Wash.AltaRock Energy Inc. has several issued patents on their technology,such as

U.S. Pat. No. 8,109,094 (SYSTEM AND METHOD FOR AQUIFER GEO-COOLING by S.Petty, filed Apr. 30, 2009 and issued Feb. 7, 2012); andU.S. Pat. No. 8,272,437 (ENHANCED GEOTHERMAL SYSTEMS AND RESERVOIROPTIMIZATION by D. Bour and S. Petty, filed Jul. 7, 2009 and issued Sep.25, 2012); and has several applications pending, such as U.S. patentapplication Ser. No. 12/432,306 (SYSTEM AND METHOD FOR USE OF PRESSUREACTUATED COLLAPSING CAPSULES SUSPENDED IN A THERMALLY EXPANDING FLUID INA SUBTERRANEAN CONTAINMENT SPACE by D. Bour, filed Apr. 29, 2009);Ser. No. 12/433,747 (METHOD AND COOLING SYSTEM FOR ELECTRIC SUBMERSIBLEPUMPS/MOTORS FOR USE IN GEOTHERMAL WELLS by S. Petty, filed Apr. 30,2009);Ser. No. 12/538,673 (METHOD FOR TESTING AN ENGINEERED GEOTHERMAL SYSTEMUSING ONE STIMULATED WELL by S. Petty, P. Rose and L. Nofziger, filedAug. 10, 2009);Ser. No. 12/754,483 (METHOD FOR MODELING FRACTURE NETWORK, AND FRACTURENETWORK GROWTH DURING STIMULATION 1N SUBSURFACE FORMATIONS, by S. Petty,M. Clyne and T. Cladouhos, filed Apr. 5, 2010);Ser. No. 12/791,735 (SYSTEM AND METHOD FOR DETERMINING THE MOSTFAVORABLE LOCATIONS FOR ENHANCED GEOTHERMAL SYSTEM APPLICATIONS, by S.Petty, O. Callahan, M. Clyne and T. Cladouhos, filed Jun. 1, 2010);Ser. No. 13/326,285 (HIGH TEMPERATURE TEMPORARY DIVERTER AND LOSTCIRCULATION MATERIAL by D. Bour, L. Watters, S. Petty and A. Apblett,filed Dec. 14, 2011); andSer. No. 13/342,924 (SYSTEM AND METHOD FOR AQUIFER GEO-COOLING by S.Petty, filed Jan. 3, 2012);which may be considered prior art for the invention disclosed in thisapplication.

However, there are some drawbacks to such prior art systems using EGS.First, energy must be expended both to force water down into theinjection well, and to pump the heated water/steam from within theEarth. Although the energy produced can still be significantly larger,it is an additional, ongoing cost. Second, EGS requires very largequantities of water to serve the needs of the injection well. In thewestern United States, the most likely area to deploy EGS becausegeothermal resources can be tapped with shallower wells, water is scarceand coveted resource. In those areas where sufficient water isavailable, additional problems arise due to the ultimate pollution ofthat water due to the minerals, salts and other toxic elements injectionwell water concentrates as it moves through the EGS cycle. Third,“fracking” in the Earth at the bottom of the injection well can releasemethane, contaminating groundwater, and creates seismic events, whichcan sometimes be felt at the surface as earthquakes. A recent EGSproject in Switzerland was suspended and ultimately cancelled due tostrong seismic events (including a magnitude 3.4 earthquake) in thenearby city of Basel triggered by the injection well [see, for example,Domenico Giardini, “Geothermal quake risks must be faced”, Nature Vol.463, p. 293 (January 2010)].

FIG. 2 illustrates a prior art alternative approach to mining heat fromdry hot rock as proposed by GTherm Inc. of Westport, Conn. In the priorart GTherm system, as in EGS, a surface facility 12-1 at the surface ofthe Earth 10 provides a pumping system 18-1 to inject water into theEarth through injection piping 14-1, and to pump water/steam from theEarth through production piping 16-1 once heated. However, in the GThermsystem, a single well shaft 11-1 with a well head 15-1 extends into theEarth to the thermal pool 560, and contains both the injection piping14-1 and the production piping 16-1. At the base of the well shaft,using underground drilling techniques such as potter drilling, developedby Potter Drilling Inc. of Redwood City, Calif. and described in part inU.S. Pat. No. 8,235,140 (METHOD AND APPARATUS FOR THERMAL DRILLING by T.Wideman, J. Potter, D. Dreesen and R. Potter, filed Oct. 8, 2009 andissued Aug. 7, 2012), a chamber 580 in the rock is formed surrounded bythe thermal pool 560, and them sealed with a coating 590 of a specialproprietary grout. This chamber 580 with coating 590 forms what GThermdesignates a “Heat Nest”.

Water is then injected through the injection piping 14-1 into thechamber 580 with coating 590, creating a reservoir of liquid 550. Thisliquid 550 heats up, and is then pumped out of the same well shaft 11-1through the production piping 16-1, either as superheated water or assteam. As in the previous EGS configuration, the heated water/steam isused to drive a production facility 20-1 to generate electricity.

This modified, single well EGS (SWEGS) closed loop approach of GThermhas some advantages over conventional EGS. First, once the heat nest hasbeen formed, no fracturing of the bedrock need occur, meaning no seismicevents will occur to disturb surface residents. Second, the waterremains confined in the heat nest, and does not mix with local watersources or become contaminated with minerals or organic compounds fromthe local soil. Third, since the water used in the thermal loop does notmix with the local sources of groundwater, groundwater contaminationdoes not occur unless there is damage or a leak to piping in the wellshaft.

Several patent applications have been filed on this SWEGS technology,including U.S. patent application Ser. No. 12/456,434 (SYSTEM AND METHODOF CAPTURING GEOTHERMAL HEAT FROM WITHIN A DRILLED WELL TO GENERATEELECTRICITY by M. Parrella, and filed Jun. 15, 2009; and

Ser. No. 12/462,656 (CONTROL SYSTEM TO MANAGE AND OPTIMIZE A GEOTHERMALELECTRIC GENERATION SYSTEM FROM ONE OR MORE WELLS THAT INDIVIDUALLYPRODUCE HEAT);Ser. No. 12/462,657 (SYSTEM AND METHOD OF MAXIMIZING HEAT TRANSFER ATTHE BOTTOM OF A WELL USING HEAT CONDUCTIVE COMPONENTS AND A PREDICTIVEMODEL);Ser. No. 12/462,658 (SYSTEM AND METHOD OF MAXIMIZING GROUT HEATCONDUCTIBILITY AND INCREASING CAUSTIC RESISTANCE); andSer. No. 12/462,661 (SYSTEM AND METHOD OF MAXIMIZING PERFORMANCE OF ASOLID-STATE CLOSED LOOP WELL HEAT EXCHANGER), all by M. Parrella andfiled Aug. 5, 2009.

Although the SWEGS variation does offer improvements over conventionalEGS, it still uses water as the fluid to carry heat from the thermalpool to the surface. As illustrated in Table I, if the temperature inthe thermal pool is below 100° C., liquid water has a large energydensity, and can do an efficient job of bringing heat to the surface.Water has a specific heat of 4.187 kJ/(kg ° C.) and a density of 1,000kg/m³, giving an appreciable energy density of 4,187 kJ/(m³° C.).However, at a pressure of 1 atmosphere (1 atm, also 1.01 bar or 101 kPa)the temperature of liquid water is at most 100° C., and therefore theamount of heat that can be raised with each kilogram of water is limitedby its boiling point.

TABLE I Table I: Specific Heat, typical Mass Density, and Energy Densityof water, steam, and various other substances. Specific Mass Energy HeatDensity Density kJ/(kg ° C.) kg/m³ kJ/(m³ ° C.) Water (20° C.) 4.1871,000 4,187 Superheated Water (161 atm, 8.138 579 4,712 350° C.) Steam(1 atm, 100° C.) 2.027 0.59 1.2 Superheated Steam (10 atm 1.623 3.95 6.4350° C.) Uranium 0.120 19,100 1,292 Granite 0.790 2,700 2,133 MoltenSalt (142-540° C.) 1.560 1,680 2,621 Aluminum (#6061) 1.256 2,710 3,404Cast Iron 0.456 7,920 3,612 Stainless Steel (Grade 316) 0.502 8,0274,030 Sources: Water:http://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlSupercritical Water: www.isa.org/~birmi/magnetrol/Technical_Handbook.pdfSteam: http://www.thermexcel.com/english/tables/vap_eau.htm SuperheatedSteam: http://www.spiraxsarco.com/esc/SH_Properties.aspx Salt/Metals:http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.htmlSteel: http://www.engineersedge.com/properties_of_metals.htm

Water can be superheated under pressure, and can have a boiling point ashigh as 374° C. under a pressure of 214 atm. Table I also shows theenergy density achievable for water superheated to 350° C. If theproduction well is suitably airtight and pressurized, highertemperatures can be maintained, and with the greater temperatureincrease, significantly more heat can be pumped to the surface whensuperheated water is used. However, such high-pressure plumbing systemsfor a well several kilometers below the surface can be difficult tomaintain. Also, superheated water can be a much better solvent forlarger organic compounds, particularly if they have some polar groups orcontain aromatic compounds, increasing the risk of contamination in thesystem. Therefore, superheated water can be more corrosive than water atordinary temperatures, and at temperatures above 300° C. specialcorrosion resistant alloys may be required for the well casing,depending on the composition of the dissolved components.

An alternative to using superheated water is to allow the waterunderground to boil and become steam. Extreme pressures need not bemaintained to control the flow of the steam at temperatures that can besignificantly hotter than 100° C. But, as shown in Table I, the energydensity of steam is significantly lower than liquid water. Even thoughthe specific heat (2.027 kJ/(kg ° C.)) is smaller by only a factor of 2,the much lower density (typically 0.6 kg/m³) of normal steam means thesame volume of steam holds 3,500 times less heat than liquid water.Supercritical heating of steam, increasing the temperature and pressure,can increase the volumetric energy density somewhat, but typically notby more than a factor of 10, and then the problems of managing anextremely hot fluid under pressure are reintroduced.

Table I also compares the energy density possible with water and steamwith a few other materials, notably molten salt (heated above 142° C.)and several metals. These support an energy density much higher thanthat of steam for cases where the thermal pool is hotter than 100° C.,especially for the case of stainless steel, where the energy densityapproaches water again.

There is therefore a need for a geothermal system which can operate as aclosed loop system without causing seismic damage or groundwatercontamination, but which also allows for a substance with a largevolumetric energy density to be used to absorb heat inside the Earthfrom depths where the temperature is greater than 100° C., coupled withan efficient means to bring the heated substance to the surface of theEarth for thermal harvesting.

BRIEF SUMMARY OF THE INVENTION

The invention disclosed with this application is a method of extractingenergy from the Earth. There are many embodiments of the inventiondisclosed here. Several embodiments of the invention comprise theinsertion of a thermal mass into a Heat Absorption Zone, having thethermal mass absorb heat while in the Heat Absorption Zone, raising thethermal mass to a Heat Transfer Zone, and transferring the heat from thethermal mass.

In some embodiments of the invention, the thermal mass comprisesinternal chambers filled with a liquid thermal absorber such as moltensalt, and the transfer of heat comprises transferring the heated liquidthermal absorber out of the thermal mass.

In some embodiments of the invention, the thermal mass comprisesstructures to facilitate heat exchange with a thermal exchange fluid,and the transfer of heat comprises flowing an exchange fluid through thethermal mass.

In some embodiments of the invention, the thermal mass is balanced witha counterweight. In some embodiments of the invention, the counterweightis another thermal mass.

In some embodiments of the invention, the heat transferred from thethermal mass can be utilized for a number of possible industrialprocesses, including generating electricity.

In some embodiments of the invention, a solid material, such as a saltmixture, is transported into a Heat Absorption Zone, where it absorbsheat and melts. The hotter melted material is then raised to a HeatTransfer Zone, and the heat is transferred from the material and used todrive a number of possible industrial processes, including generatingelectricity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a schematic overview of an example of prior art enhancedgeothermal systems (EGS) for geothermal energy extraction.

FIG. 2 presents a schematic overview of a prior art single-well enhancedgeothermal system (SWEGS) using a thermal nest for geothermal energyextraction.

FIG. 3 presents a flow diagram of the thermal extraction processaccording to several embodiments of the invention.

FIG. 4 presents a schematic overview of one embodiment of the invention.

FIG. 5 presents in more detail a cross section view of an embodiment ofthe invention in which a thermal mass is being heated.

FIG. 6 presents in more detail a cross section view of the embodiment ofthe invention shown in FIG. 5 in which the thermal mass has been raisedto the surface and heat is being transferred from thermal mass to athermal reservoir.

FIG. 7 presents a cross section view of an embodiment of the inventionthat uses a thermal fluid to transfer the heat from the thermal mass.

FIG. 8 presents an external shell for a thermal mass according to theinvention.

FIG. 9 presents the internal and top parts of a thermal mass accordingto a first embodiment of the invention.

FIG. 10 presents a mechanism for mechanical support of the thermal massaccording to the invention.

FIG. 11 presents a cross section view of an embodiment of the inventionthat uses a thermal exchange fluid to transfer the heat from the thermalmass.

FIG. 12 presents the internal and top parts of a thermal mass accordingto a second embodiment of the invention.

FIG. 13 presents the internal and top parts of a thermal mass accordingto a variation of the second embodiment of the invention.

FIG. 14 presents a flow diagram of the first part of a process accordingto an embodiment of the invention in which two thermal masses are used.

FIG. 15 presents a flow diagram of the second part of a processaccording to an embodiment of the invention in which two thermal massesare used.

FIG. 16 presents a schematic overview of an embodiment of the inventionin which two thermal masses are used.

FIG. 17 presents in more detail a cross section view of the embodimentof the invention shown in FIG. 16 in which two thermal masses are used.

FIG. 18 presents a schematic overview of an embodiment of the inventionin which two thermal masses are used in the same well.

FIG. 19 presents a schematic overview of an embodiment of the inventionusing a closed loop for a thermal substance and comprising a screw alongthe length of the injection well.

FIG. 20 presents a schematic overview of an embodiment of the inventionusing a closed loop for a thermal substance and comprising a ram screwin the Heat Absorption Zone.

Note that the illustrations provided are for the purpose of illustratinghow to make and use the invention, and are not to scale. The wells areanticipated to be kilometers deep, while the thermal masses are expectedto be typically 50 centimeters to 30 meters long and from 10 to 100centimeters in diameter, and can be scaled to be other sizes and shapesif desired.

DETAILED DESCRIPTIONS OF EMBODIMENTS OF THE INVENTION

What follows are detailed descriptions of several embodiments of theinvention, including embodiments believed by the inventor to be the bestmode.

Common to many embodiments of the invention are the steps illustrated inthe flow diagram of FIG. 3 and the overview illustration shown in FIG.4. To start, as shown in FIG. 3, the initial step 2000 comprises digginga well shaft 60 into the Earth, until a portion of the well shaft 60 issurrounded by a thermal pool 560. It should be noted that someembodiments of the invention could be implemented in a pre-existingwell, so that a new well shaft 60 need not be dug for each installation.

In the second step 2100, a thermal mass 100 is then prepared with aprocedure that typically comprises attaching it to a suspension cable140 which in turn is attached to a control system 148 for raising andlowering the thermal mass 100. Once the thermal mass has been prepared,in the next step 2200 the thermal mass 100 is then lowered down the wellshaft 60 until it reaches the thermal pool 560. This region isdesignated the Heat Absorption Zone. The next step 2300 comprisesallowing the thermal mass 100 to remain in the Heat Absorption Zoneuntil a desired temperature is reached or a predetermined amount of heathas been absorbed by the thermal mass 100. The illustration in FIG. 4represents the process at this point.

After this, the next step 2400 comprises raising the heated thermal mass100 to an area designated the Heat Transfer Zone, typically near thesurface of the Earth 10. The next step 2500 comprises extracting theheat energy from the thermal mass 100 and transferring it to a thermalreservoir 200. After this, the thermal mass 100 can be prepared againaccording to a repetition of the second step 2100 and the subsequentsteps 2200 through 2500 repeated, and the cycle continues.

At the same time, according to alternative step 2800, the heat energytransferred into the thermal reservoir 200 can be used in a productionfacility 250 for a number of useful processes, such as generatingelectricity, driving another industrial process such as pyrolysis, orsimply being stored for later use. A housing 25 or other structure toprotect the well shaft 60 from the elements can also be constructed,either independent of, or in connection with the production facility250.

For the purposes of this description, the term “thermal mass” can be anydiscrete object, whether it be solid, hollow, liquid filled, etc. thathas a mass and a heat capacity and is prepared for insertion into thethermal well. It can be a simple slug of metal, chosen for its heatcapacity, or a more complex structure with internal mechanisms, pipingand structures, and may additionally comprise reservoirs of fluids andplumbing to facilitate the transfer of heat by the transfer of fluidsinto and out of the thermal mass. It may also contain chambers or otherstructures to facilitate an internal chemical process.

The preparation of the thermal mass can be a procedure as simple asattaching it to a cable for suspension. However, if there are morecomplex internal structures, such as internal piping and reservoirs, thepreparation can also comprise checking the temperatures, pressures, filllevels and purity of fluids in the chambers, the distribution of mass,making an exchange of fluids needing replacing, confirming the conditionof the seals on the valves and connectors, corrosion, inspection forcracks or other damage on the external shell or the suspension cables,determining the security of any hoses and seals, the calibration of anygauges or data sensors, etc.

For the purposes of this description, the term “thermal pool” refers toa portion of the Earth underground that is significantly hotter than atthe surface, and which therefore provides a source of energy. Althoughthe thermal pool as described in the embodiments of the inventiondisclosed here will generally be a stratum of hot dry rock as might beused in the prior art EGS configurations, these embodiments may also beapplied to any geothermal heat source, including to wells which extenddeep enough to encounter molten rock or magma within the Earth.

For the purposes of this description, the term “thermal well” refers tothe Heat Absorption Zone, and describes a structure created in theEarth, typically by drilling a hole, in which at least a portion of thestructure, typically the bottom, is in the thermal pool, and istherefore naturally at a significantly hotter temperature than is foundon the surface of the Earth. When an object, such as the thermal mass,is inserted into the thermal well and left there, the object heats up asit is surrounded by the thermal pool.

A First Embodiment of the Invention

One embodiment of the invention is illustrated in more detail in FIG. 5and FIG. 6. Note that these illustrations are not to scale, since thewells are anticipated to be kilometers deep while the thermal masses areexpected to be, for example, 1 to 30 meters long and perhaps 50 to 100centimeters in diameter.

In this embodiment of the invention, the deeper part of the well shaft60 surrounded by the thermal pool 560, can be lined with a thermalcasing 64 that facilitates the transfer of heat from the thermal pool560 to the thermal mass 100. This thermal casing can be made using amaterial such as a thermally conducting grout, often made fromcompositions comprising water, cement, siliceous gel, and sometimesbentonite. Additional materials such as iron filings or other metallicpowders can be mixed into the grout to enhance thermal conductivity. Thesurface can also be treated to be smooth to increase emissivity forenhancing radiative heat transfer. Although the well shaft as shown is asimple vertical hole, the well shaft can have more complex structuressuch as varying diameters, chambers situated at various positions alongthe shaft, or side tunnels.

Likewise, the upper part of the well shaft 60, which is at coolertemperatures, can be lined with an insulating casing 62 that preventsheat from the thermal mass 100 from dissipating before it reaches thetop of the well shaft 60. This insulating casing can be made using amaterial such as solid concrete, porous concrete, tubing walls of ⅜″thick stainless steel, or a layered structure of concrete and steel. Forinsulation in high heat situations, a weave of basalt fabrics such asthose manufactured by Smarter Building Systems of Newport, R.I. mayprovide an adequate insulating casing. Other fiber products comprisingceramic or silica materials can also be used.

The system also comprises suspension mechanism such as a suspensioncable 140 or other suspension rigging that suspends the thermal mass 100in the well shaft 60. The suspension cable 140 can be attached to asuspension mechanism 141 for raising and lowering the suspension cable140 and the attached thermal mass 100, which in turn is managed by acontrol system 148. The system can also comprise an additionalcommunication cable 142 with a data connector 132 to sensors in thethermal mass 100 that provide data about variables of interest such astemperature, thermal expansion, distribution of mass, etc. Thiscommunication cable 142 can be managed using independent mechanism 143that winds and unwinds the communication cable 142 as the thermal mass100 is lowered and raised. In some embodiments, the communication cablecan instead be integrated into the suspension cable 140, and raised andlowered using the suspension mechanism 141. A housing 25 can be providedto protect the machinery for raising and lowering the thermal mass 100from the elements.

In some embodiments of the invention, a thermal transfer system in theHeat Transfer Zone will also be provided to unload the heat in thethermal mass 100. In some embodiments, heated fluid from the thermalmass 100 is transferred through a thermal transfer conduit 150, whichcan in some embodiments have a moving or telescoping junction 152 toconnect with the thermal mass 100 using a thermal fluid connector 135.The heated fluid is then transferred to a thermal reservoir 200contained in a thermal reservoir containment 180. The heat in thethermal reservoir 200 is then used to generate electricity or drive anindustrial process in a production facility 250, which can comprise ameans for generating electricity 257 or other production equipment.

In some embodiments of the invention, the heat can be transferred bydetaching the thermal mass 100 from the suspension cable 140 and placingthe hot thermal mass 100 into a thermal reservoir 200 for subsequentthermal transfer. If the thermal mass 100 is designed as a simple slugof metal with a large heat capacity, this transfer can comprise placingthe hot thermal mass into a fluid bath in the thermal reservoir 200, inwhich the heat is transferred from the thermal mass to the fluid in thebath. If the thermal mass 100 is a metallic structure with more complexinternal structures, such as internal tubes that facilitate fluid flowfor heat transfer through the thermal mass 100, the thermal mass 100 canbe attached to a plumbing system that provides fluid that removes theheat from the inside of the thermal mass 100 as it passes through thevarious internal tubes.

In the meantime, while the initial thermal mass 100 is transferring heatin the Heat Transfer Zone, an alternate thermal mass, which willtypically be an object with dimensions and a construction similar to theinitial thermal mass 100, can be attached to the suspension cable 140and lowered into the well shaft 60 to begin heating in the HeatAbsorption Zone.

FIG. 7 provides a more detailed illustration of one embodiment of theinvention. For this embodiment, the thermal mass 100 comprises a hollowcavity, typically cylindrical in shape, which is filled to apredetermined level with a thermal fluid 55. The fluid can be liquidwater if used in a relatively cool well below 100° C.; or a molten saltor combination of salts, such as, for example, CN—K (Potassium CalciumNitrate—KNO₃ 5 Ca(NO₃)₂ 10 H₂O) as offered by Yara International ASA ofNorway for warmer wells, (e.g. 150° C. to 500° C.); or, for highertemperatures (e.g. 300° C. to 1000° C.) a molten salt mixture such asone comprising by weight 50% Potassium Nitrate (KNO₃), 40% SodiumNitrite (NaNO₂) and 7% Sodium Nitrate (NaNO₃). Other mixtures of saltscan be used, comprising salts such as sodium fluoride (NaF), sodiumchloride (NaCl), potassium fluoride (KF), potassium chloride (KCl)(which melt at even higher temperatures) as long as their proportionsare managed to provide an appropriate thermal and fluid properties forthe temperature of the thermal pool 560. Mixtures of molten salts usedfor energy storage and transport in the concentrated solar power (CSP)facilities may also be adapted for use in the embodiments of theinvention disclosed here.

During the preparation of the thermal mass 100, the hollow interior ofthe thermal mass 100 is provided with thermal fluid 55 from a coolthermal fluid reservoir 202 which will typically contain previouslycooled fluid 55-C. This cool thermal fluid reservoir 202 will typicallybe constructed in the thermal reservoir containment 180, which alsocontains the thermal reservoir 200 for heated thermal fluid 55-H. Thefilling process for the thermal mass 100 can be controlled by a pumpingsystem 155 through a valve on the cool thermal fluid reservoir 202 and avalve 185 that switches the pumping system 155 between the cool thermalfluid reservoir 202 and the thermal reservoir 200. The fluid 55 isprovided to the thermal mass 100 through thermal transfer conduit 150through the moving or telescoping junction 152 which connects to thethermal mass 100 at the thermal fluid connector 135. The thermal mass100 in some embodiments will comprise an interior transfer tube 115connected to the thermal fluid connector 135 that extends to near thebottom of the reservoir within thermal mass.

Since hot fluids, and in particular a molten salt system, can degraderapidly when exposed to air, and additionally can be corrosive anddangerous, it may be advisable to seal the thermal fluid from exposureto the ambient environment. In that case, there can be an additionalsystem to provide a cover gas 56 compatible with the thermal fluid 55 toallow fluid levels to vary without venting the system to outside air.Such a cover gas system would include a cover gas manager 160,comprising a cover gas reservoir 165 and a cover gas pumping system 162to provide cover gas 56 to the thermal mass 100 through a valve 163 andpiping 164, which connects to the thermal mass 100 at a cover gasconnector 136, or to provide cover gas 56 to the thermal reservoircontainment 180 through a valve 167 and piping 168.

The thermal mass 100 may also comprise sensors such as a temperaturesensor 122 connected to an internal data cable 123 that connects at adata connector 132 to the communication cable 142. The selection of theexact materials used in the temperature sensor 122 may be different,depending on the selection of thermal fluid 55 and the temperatureincreases expected. In particular, any sensors that are used must beable to operate at the heightened temperatures expected to be found inthe thermal pool 560, which may routinely exceed 500° C. and may in someembodiments be nearly as hot as molten magma. For lower temperaturethermal pools 560, conventional thermocouples may be employed in thetemperature sensor 122. For embodiments with high temperatures, manymetals melt, and sensors comprising complex circuits can no longerfunction. For these situations, simpler systems such as a platinumresistance thermometer may be employed as the temperature sensor 122.For extremely hot temperatures, a dual metal (two component) thermostatmay be employed, simply making electrical contact to close a circuitonce a predetermined calibrated temperature has been reached. Othertemperature sensor options may be known to those skilled in the art.

The thermal mass may also comprise other sensors, including but notrestricted to motion sensors, accelerometers, acoustic sensors, opticalsensors, infrared sensors, fluorescence sensors, pressure sensors, andsensors for temperature gradients. The connections for the varioussensors can be through electrical wires to the communications cable 142,through a fiber optic connector, or through wireless transceivers. Theonly major consideration limiting selection among these various optionsis their ability to function under the temperature conditions found whenthe thermal mass 100 has been immersed in the thermal pool 560.

Once the thermal mass 100 has been heated in the thermal pool 560 andreturned to the Heat Transfer Zone, the moving or telescoping junction152 can be joined at the thermal fluid connector 135 to the internaltransfer tube 115 within the thermal mass 100. The internal transfertube 115 provides a means of evacuating the thermal fluid 55 from thethermal mass 100 through the thermal transfer conduit 150, which canalso comprise a pumping system 155 to pump the thermal fluid 55 from thethermal mass 100 into the thermal reservoir 200. This pumping system 155and conduit 150 can be the same pumping system and conduit previouslyused to fill the thermal mass, or in some embodiments separate pumpingsystems and conduits may be designed to provide an alternative flowchannel. A valve 175 controls the flow of thermal fluid into the thermalreservoir through valve 185, which can be closed once the transfer hasbeen completed. In some embodiments, the thermal transfer conduit 150and components of the pumping system 155 as well as other components incontact with the thermal fluid may be coated with a suitable materialsuch as Nichrome to prevent corrosion.

Once transferred to the thermal reservoir 200, the hot thermal fluid55-H in the thermal reservoir 200 can then be used to generateelectricity or drive another industrial process such as pyrolysis in aproduction facility 250, which can comprise a means for generatingelectricity 257 or some other production equipment. Once its heat hasbeen extracted and used, the cooled thermal fluid 55-C can be returnedto a cool thermal fluid reservoir 202, where it serves as a source ofthermal fluid 55 for refilling the thermal mass 100.

FIG. 8 shows an example of one embodiment for the external parts of anassembly for a thermal mass 100. The exterior shell 101 in this exampleis a cylindrical tube, sealed at the bottom, and can be manufacturedfrom a chromium alloy steel such as duplex SAE grade 2205 stainlesssteel if the thermal mass is to be used at temperatures lower than 300°C., while a corrosion resistant steel also containing molybdenum such asSAE grade 254SMO can be used for hotter temperatures. The thickness mayvary depending on the overall weight and design considerations, but itis expected that a thickness of 1 cm (⅜″) or larger for the wallthickness will be typical. The thermal mass 100 is also expected totypically be as large as 1 meter in diameter, and may be as long as 30meters. The inner and/or outer surface of the exterior shell 101 canalso be coated with an alloy such as nichrome to help prevent corrosion.

To facilitate centering in the well shaft 60, the outside of thecylindrical shell may be provided with several spacers 103 designed tobe able to bump against the side of the well as the thermal mass 100descends and ascends. The spacers 103 can be simple metallic structuresacting as springs welded onto the side of the exterior shell 101, or canbe more complex structures, comprising rollers or other mechanismsdesigned to reduce the friction with the wall of the well shaft 60.

The bottom of the exterior shell 101 can comprise structures 108 such asa ring or a flange that provide a means for supporting the bottom of thethermal mass 100 such as apertures 105 for attaching cables. Thesestructures 108 may be welded to the exterior shell 101, held by means ofa threaded grooves cut into the side of the exterior shell 101, orattached by some other means known to those skilled in the art. The topof the exterior shell 101 may comprise a shell flange 109 comprising anumber of apertures 102 that can be used to seal the top of the thermalmass 100 using a sealing method such as a stainless steel O-ring, inwhich the shell flange 109 is bolted to a mating top flange through theapertures 102 in a manner that crushes the O-ring, making a seal. Theonly requirement is that this sealing method be able to withstand thetemperatures and pressures that the thermal mass 100 will be subjectedto in the thermal pool 560.

FIG. 9 shows the complementary part of the thermal mass 100, comprisingthe top flange 110 and also several internal structures. The top flange110 is designed to be mated to the shell flange 109 shown in FIG. 8,with apertures 112 in the top flange 110 aligned with the apertures 102in the shell flange 109.

As shown in FIG. 9, the top flange 110 is larger in diameter than shellflange 109, and additionally comprises apertures 114 that provide ameans of suspending the top of the thermal mass 100 from the suspensioncable 140.

As shown in FIG. 9, the top flange 110 also comprises the variousfeedthroughs that connect the thermal mass 100 to various systems. Thethermal fluid connector 135 is attached to the internal transfer tube115 and is designed to mate with the moving or telescoping junction 152to transfer the thermal fluid 55 into and out of the thermal mass 100.The cover gas connector 136 is attached to an internal cover gas tube116 and is designed to mate with the piping 164 that provides cover gas56 from the cover gas manager 160. The data connector 132 is attached toan internal data cable 123 that connects to internal sensors, such as atemperature sensor 122, and is designed to mate with the communicationcable 142 that provides information about the thermal mass 100 to thecontrol system 148.

As shown in FIG. 9, the internal structures can also comprise internalspacers 113 that hold the various internal elements such as the internaltransfer tube 115 for thermal fluid and the internal data cable 123 inplace. The internal structures can also comprise a shoe 125 at thebottom of the internal transfer tube 115 that adjusts the flow directionof the thermal fluid 55 as it enters and exits the thermal mass 100.

FIG. 10 shows one embodiment of the invention in which the assembledthermal mass 100 has been suspended from the suspension cable 140. Inthis illustration, the suspension cable 140 is split at the couplingmechanism 138 into eight smaller suspension cables 144, each withattachment mechanisms 145 such as hooks or fasteners. In the embodimentof FIG. 10, four of these cables 144-U are shorter, and attach to fourof the apertures 114 in the top flange 110 using hooks 145-U. The otherfour cables 144-L are longer, and pass through the other apertures 114in the top flange 110 and extend to the apertures 105 in the structures108 attached to the lower portion of the thermal mass exterior shell 101using hooks 145-L.

Although FIG. 10 presents one embodiment for suspending the thermal mass100, it will be clear to those skilled in the art that several differentsuspension mechanisms can be devised which will still conform with theembodiments of the invention as described in this section. In oneembodiment, a web of cables can support the thermal mass at a pluralityof points. In one embodiment, the thermal mass can be contained in a netof cables that is suspended from the suspension cable 140. In oneembodiment, the spacers 103 can be integrated into the suspension systemto provide additional points of attachment for the smaller suspensioncables 144 that merge to form the suspension cable 140. In otherembodiments, the thermal mass itself may comprise steel rods orattachment mechanisms designed to mate with one or more attachmentmechanisms, such as hooks, suspended from the suspension cable 140.

If will also be clear to those skilled in the art that the illustrationin FIG. 10 is not necessarily to scale. The thermal mass can, forexample, have a diameter as small as 1 cm or as large as 1 meter, aswell as a length as small as 25 centimeters or as large as 30 meters oreven larger, depending on the size and scale of the well and the liftingmechanism. It will also be clear to those skilled in the art that someembodiments of the invention may be engineered in which the thermal massis more aerodynamically streamlined than illustrated in FIG. 10. A morestreamlined design will reduce air drag on the thermal mass 100 as it islowered into or hauled out of the well shaft 60, accelerating the energytransfer process.

It should also be noted that, although we have described this embodimentas using a cable as the mean of suspension, it will be known to thoseskilled in the art that ropes, chains, cords, wires, fabrics, fibers,nets, and other means of suspension can be used to support the thermalmasses.

A Second Embodiment of the Invention

FIG. 11, FIG. 12 and FIG. 13 show an alternative embodiment of theinvention. In this embodiment, as in the first embodiment, a well shaft60 can be dug to a thermal pool 560. As before, the well shaft 60 can belined with various casings, such as an insulating casing 62 in the upperportions of the shaft and a thermal casing 64 in the lower portion ofthe shaft. As before, a thermal mass 100-2 is lowered on a suspensioncable 140 to a Heat Absorption Zone, heated by the thermal pool 560.After heating, the thermal mass 100-2 is then raised to a Heat transferZone near the surface of the Earth 10, and the heat unloaded into athermal reservoir 300 contained in a thermal reservoir containment 380.The thermal mass 100-2 again comprises a cylindrical exterior shell 101,which can be the same design as was illustrated for the previousembodiment in FIG. 8, and can also have an interior cavity containing athermal fluid 55 covered with a cover gas 56.

However, in this embodiment, the thermal fluid 55 remains in the thermalmass 100-2, and the thermal mass 100-2 is designed with an internalchannel comprising internal piping 333 designed to have a significantsurface area in contact with the thermal fluid 55. The internal piping333 facilitates the flow of a thermal transfer fluid 35 from a thermalreservoir containment 380 containing a thermal reservoir 300. Thethermal transfer fluid absorbs heat as it flows through the internalpiping 333 of the thermal mass 100-2. The thermal transfer fluid 35 canbe a liquid, such as water, or one of many glycol-based fluids such asDOWTHERM™ (from Dow Chemical Company of Midland, Mich.), or be selectedfrom a variety of proprietary fluids such as Duratherm S (offered forsale by Duratherm Extended Life Fluids of Lewiston, N.Y.) or Dynalene HT(offered for sale by Dynalene Inc. of Whitehall, Pa.); or be a moltensalt mixture such as CN—K (Potassium Calcium Nitrate—KNO₃ 5 Ca(NO₃)₂ 10H₂O) (offered for sale by Yara International ASA of Norway), orconventional molten salts comprising various mixtures of nitrates andnitrides used in the concentrated solar power (CSP) industry. Theexchange fluid can also be a gas, such as nitrogen, argon, helium, orcompressed carbon dioxide.

After the thermal mass 100-2 has been warmed in the thermal pool 560 andbrought back to the surface, the internal piping 333 can be attachedusing intake junction 338 to the thermal transfer fluid input conduit350 and outflow junction 339 to the outflow conduit 352. A pumpingsystem 355 facilitates the transfer of the thermal transfer fluid 35through the thermal mass 100-2 to the thermal reservoir 300 throughexport valve 389. The heated thermal transfer fluid 35-H in the thermalreservoir 300 can then be used to generate electricity or drive anotherindustrial process such as pyrolysis in a production facility 250, whichcan comprise a means for generating electricity 257 or some otherproduction equipment. Once its heat has been extracted and used, thecooled thermal transfer fluid 35-C can be returned to a cool thermalfluid reservoir 302, where it serves as a source of thermal fluid 35 forrefilling the thermal mass 100-2.

FIG. 12 shows an example of one embodiment for the internal parts of anassembly for a thermal mass 100-2 designed to use a thermal transferfluid 35. As in the previously described embodiment, a top flange 310has been designed to mate with shell flange 109, and apertures 312 intop flange 310 are designed to correspond to the apertures 102 in shellflange 109 for sealing using a sealing method such as a stainless steelO-ring, as described in a previous embodiment.

However, in this embodiment, the top of the thermal mass 100-2 willcomprise an intake junction 338 where thermal transfer fluid 35 entersthe internal piping 333 of the thermal mass 100-2. The thermal transferfluid heats up as it flows through the internal piping 333, which inthis illustration is shown as a double helix structure. Heated thermaltransfer fluid 35 then flows out of an outflow junction 339 where thethermal transfer fluid exits the internal piping 333 of thermal mass100-2.

FIG. 13 shows an additional example of one embodiment for the internalparts of an assembly for a thermal mass 100-2 designed to use a thermaltransfer fluid. As in the embodiment illustrated in FIG. 12, the thermalmass 100-2 comprises internal piping 433 to facilitate heat transfer,and comprises a top flange 310 that has been designed to mate with shellflange 109, and apertures 312 in the top flange 310 are designed tocorrespond to the apertures 102 in shell flange 109 for sealing using asealing method such as a stainless steel O-ring, as described in aprevious embodiment.

As in the embodiment of FIG. 12, thermal exchange fluid will be providedto the thermal mass 100-2 through an intake junction 438 where thermaltransfer fluid enters the internal piping 433 of the thermal mass 100-2.The thermal transfer fluid heats up as it flows through the internalpiping 433, but in this case the piping comprises a straight inflow pipedirectly to the bottom of the thermal mass 100-2, and a helical returnpath to the top. The heated thermal transfer fluid 35 flows out throughan outflow junction 439 where the thermal transfer fluid exits theinternal piping 433 of thermal mass 100-2

Note that, although a temperature sensor can be used in this embodimentto monitor the thermal mass, it is not expected that a temperaturesensor inside the thermal mass is necessary for these embodiments of theinvention. Instead, the temperature of the thermal exchange fluid 35 canbe monitored as the heat is transferred.

It should also be noted that one possible variation on this embodimenthas no thermal fluid 55 filling the thermal mass. Instead, the thermalmass 100-3 is simply filled with a solid material having a large heatcapacity, such as granite, iron or stainless steel surrounding theinternal piping 333. The solid material can be a cast solid, such ascast iron, or an ensemble of solid objects such as granite sand or smallball bearings.

It should also be clear that, although internal channels comprisingpiping in the form of a helix or a double helix have been illustrated,other configurations are also possible. Channels normally used in heatexchangers, such as a serpentine form in which the piping forms a zigzagpattern, or a conventional spiral coil can also be used. Likewise, itshould also be noted that the connections to the internal channel,although shown as separate connectors in FIG. 12 and FIG. 13, could bedesigned as a single connector that can accommodate both the insertionand the removal of the thermal exchange fluid.

A Third Embodiment of the Invention

In the previously described embodiments, the thermal mass can be loweredinto the thermal well and then raised once it has acquired heat.However, for a single thermal mass raised into a single thermal well,significant energy must be expended to raise the thermal mass againstthe pull of gravity. This may place a practical limit on the mass thatcan be used, since a thermal mass that is heavier will require moreenergy to raise, especially when the wells are at depths of kilometers.However, heavier masses may be advantageous from a thermal energy pointof view, in that heavier, denser thermal masses can have a significantlylarger heat capacity, and therefore acquire more heat to be harvestedonce the thermal mass is returned to the surface.

An alternative embodiment of the invention can mitigate the energyexpenditure required to raise warmed thermal masses from the thermalwell. In this embodiment, at least two (2) paired thermal masses areconnected by a single suspension cable, and serve as counter-weights foreach other. Therefore, as one thermal mass is pulled down by gravity, itpulls its companion thermal mass up out of its thermal well.

Such counter-weight systems are commonly applied to the raising andlowering of construction materials for cranes, in the design of bridges,and the like. If the two thermal masses and cables are well matched, theonly energy that need be lost to raise a thermal mass from a thermalwells is the energy to overcome the friction of the cables against theirmechanisms, and the air resistance as the thermal masses are raised andlowered. Proper lubrication can reduce the energy losses due tofriction, while aerodynamic design of the thermal masses can help reducethe drag encountered when the thermal mass is raised and lowered in thewell shaft.

The steps for this embodiment of the invention are illustrated in theflow diagrams of FIG. 14 and FIG. 15 and the overview cross-sectiondiagram shown in FIG. 16. Note that the illustrations shown here are notto scale. The wells are anticipated to be kilometers deep, while thethermal masses are expected to be, for example, 50 centimeters to 30meters long and perhaps 10 centimeters to 1 meter in diameter.

To start, as shown in FIG. 13, the initial step 3000 comprises diggingwell shafts 60 and 1060 into the Earth, until a portion of each wellshaft 60 and 1060 is surrounded by a thermal pool 560, formingrespective first and second Heat Absorption Zones. In the next step3050, one end of the suspension cable 1140 is unwound, and in the thirdstep 3100, a thermal mass 100 is then prepared with a procedure thattypically comprises attaching it to one end of the suspension cable1140, which in turn is attached to a control system 1148 for raising andlowering the thermal mass 100.

Once the thermal mass 100 has been prepared, in the next step 3200 thethermal mass 100 is then lowered down the well shaft 60 until it reachesthe first Heat Absorption Zone heated by the thermal pool 560. Afterthat, the next step 3300 comprises allowing the thermal mass 100 toremain surrounded in the first Heat Absorption Zone until a desiredtemperature is reached or a predetermined amount of heat has beentransferred to the thermal mass 100.

In the meantime, near the surface of the Earth 10, a parallel step 3150comprising unwinding the other end of the suspension cable 1140 occurs,and the second thermal mass 1100 is then prepared with a procedure step3160 that typically comprises attaching it to the suspension cable 1140which in turn is attached to the control system 1148 for raising andlowering the second thermal mass 1100.

After this, the next step 3400 as shown in continuation flow chart ofFIG. 15 comprises raising the heated thermal mass 100 to the first HeatTransfer Zone near the surface of the Earth 10 while simultaneouslylowering the second thermal mass 1100 into the second Heat AbsorptionZone of a second well shaft 1060. By having the two thermal massescounterbalancing each other, the energy supplied by gravity to lower thesecond thermal mass 1100 pulls the first thermal mass 100 up the firstwell shaft 60, and therefore the only energy that need be supplied todrive the process is the energy to overcome friction and aerodynamicresistance of the thermal masses 100 and 1100 in their respective wellshafts 60 and 1060.

The next step 3530 comprises allowing the thermal mass 1100 to remain inthe second Heat Absorption Zone heated by the thermal pool 560 until adesired temperature is reached or a predetermined amount of heat hasbeen absorbed by the thermal mass 100. In the meantime, in the firstHeat Transfer Zone near the surface of the Earth 10, an alternative step3500 executed in parallel comprises extracting the heat energy from thethermal mass 100 and transferring it to a thermal reservoir 200-2. Oncethe heat has been transferred from the thermal mass 100, the thermalmass 100 can be prepared according to the next alternative step 3550 forre-insertion into the well shaft 60.

After this, the next step 3600 comprises raising the heated secondthermal mass 1100 to the second Heat Transfer Zone near the surface ofthe Earth 10 while at the same time lowering the first thermal mass 100to the first Heat Absorption Zone of its well shaft 60. By having thetwo thermal masses counterbalancing each other, the energy supplied bygravity to pull the first thermal mass 100 down pulls the second thermalmass 1100 up the second well shaft 1060, and therefore the only energythat need be supplied to drive the process is the energy to overcomefriction and aerodynamic resistance of the thermal masses 1100 and 100in their respective well shafts 1060 and 60.

The next step 3730 comprises allowing the first thermal mass 100 toremain in the first Heat Absorption Zone heated by the thermal pool 560until a desired temperature is reached or a predetermined amount of heathas been transferred to the thermal mass 100. In the meantime, in thesecond Heat Transfer Zone near the surface of the Earth 10, a parallelstep 3700 comprises extracting the heat energy from the second thermalmass 1100 and transferring it to a thermal reservoir 200-2. Once theheat has been transferred from the thermal mass 100, the second thermalmass 1100 can be prepared again according to the next alternative step3750 for re-insertion into the well shaft 60. Then, in a repetition ofthe previous step 3400, the heated thermal mass 100 is raised to thefirst Heat Transfer Zone while the second thermal mass 1100 issimultaneously lowered into the second Heat Absorption Zone of thesecond well shaft 1060, and with the subsequent repetition of thefollowing steps 3500 through 3750, the cycle continues.

In the meantime, according to an alternative step 3800, the heat energyso transferred into the thermal reservoir 200-2 can be used for a numberof useful processes, such as generating electricity, driving anotherindustrial process such as pyrolysis, or simply being stored for lateruse in a production facility 250. A housing 1025 or other structure toprotect the well shafts 60 and 1060 from the elements can also beconstructed, either independent of, or in connection with the productionfacility 250.

FIG. 16 shows an overview schematic of a counterbalance system accordingto the invention. As before, a well shaft 60 has been drilled from thesurface of the Earth 10 into the Earth so that a portion of the wellshaft 60 is surrounded by a thermal pool 560, creating a Heat AbsorptionZone. As before, the well shaft 60 can be lined with various casings,such as an insulating casing 62 in the upper portions of the shaft and athermal casing 64 in the lower portion of the shaft. As before, athermal mass 100, such as one described in the previous embodiments, israised and lowered into the well shaft 60 on a suspension cable 1140.Heat can be transferred by one of the mechanisms described in theprevious embodiments, such as complete detachment of the thermal mass100, the transfer of a heated thermal fluid 55, or through the use of athermal exchange fluid 35.

However, in this case, the suspension cable 1140 is also attached to asecond thermal mass 1100 which is raised and lowered into a second wellshaft 1060 that also has a portion of the well shaft 1060 surrounded bythe thermal pool 560. This well shaft 1060 can also be lined withvarious casings, such as an insulating casing 62 in the upper portionsof the shaft and a thermal casing 64 in the lower portion of the shaft.Typically, this second thermal mass 1100 would be of a matched type anddesign to the thermal mass 100, although variations may be desirable ifsome properties of the second well shaft 1060 differ from those of theinitial thermal well shaft 60. A control system 1148 is used to controlthe mutual raising and lowering of the thermal masses in theirrespective well shafts 60 and 1060.

As in the previous embodiments, the thermal energy brought up with theinitial thermal mass 100 or the second thermal mass 1100 can be used togenerate electricity or drive another industrial process such aspyrolysis in a production facility 250. A housing 1025 or otherstructure to protect the well shafts 60 and 1060 from the elements canalso be constructed, either independent of, or in connection with theproduction facility 250.

FIG. 17 shows a schematic of a counterbalance system according to theinvention in more detail. Note that the illustration is not to scale,since the wells are anticipated to be kilometers deep while the thermalmasses are expected to be 50 centimeters to 30 meters long.

In FIG. 17, as in the embodiment of FIG. 6, the thermal mass 100 hasbeen raised to the surface and connected to the thermal reservoir 200-2contained in a thermal reservoir containment 180 through the thermaltransfer conduit 150 with a moving or telescoping junction 152 thatconnects using the thermal fluid connector 135. The suspension cable1140 raises and lowers the thermal mass 100 and correspondingly lowersand raises the second thermal mass 1100, driven by a suspensionmechanism 1141 that is controlled by a control system 1148.

As illustrated in FIG. 17, the second thermal mass will also require ameans to unload its heat to the thermal reservoir 200-2, and in thisillustration this is provided with a second thermal transfer conduit1150 with a second telescoping junction 1152 that connects using theconnector 1135 which is attached to the second thermal mass 1100 when itin turn has been raised near the surface of the Earth.

As in the previously described embodiments, it may be desired to havevarious sensors within the thermal masses. To facilitate thecommunication of data from these sensors on properties such astemperature, acceleration, distribution of mass, etc., a communicationcable 942 driven by an independent mechanism 943 for the first thermalmass 100 and another communication cable 1142 driven by anotherindependent mechanism 1143 for the second thermal mass 1100 may be used.These cables can be independently driven, or driven in concert by thecontrol system 1148 that also controls the raising and lowering of thethermal masses 100 and 1100.

FIG. 18 illustrates a variation of this embodiment of the invention, inwhich a counterbalance system comprising two thermal masses is used, butonly one well shaft 2060 need be drilled. As in the previousembodiments, the well shaft 2060 can be lined with various casings, suchas an insulating casing 62 in the upper portions of the shaft and athermal casing 64 in the lower portion of the shaft. As before, there isan initial thermal mass 100 and a second thermal mass 1100, bothattached to alternate ends of a suspension cable 1140. One thermal massis raised from the thermal pool 560 while the other is lowered into thethermal pool 560, and the energy of gravity used to pull one weight downin turn is used to pull the other weight up. However, in this variation,a single well shaft 2060 has been dug, and the initial thermal mass 100and the second thermal mass 1100 go up and down on different sides of asingle well shaft 2060. This can reduce costs, as only one shaft need beprepared, but may add complexity to the structures within the shaft.

If should be noted that, although we have described this embodiment asusing one cable as the means of suspension, it will be known to thoseskilled in the art that ropes, chains, cords, wires, fibers, fabrics,nets, and other means of mutual suspension can be used to support thetwo counterbalanced thermal masses.

Additional Variations of the Invention

Although certain detailed embodiments have been described in thisdisclosure and illustrated in these drawings, it will be clear that someof the elements of other technologies, such as EGS, can also be combinedwith the embodiments described here. For example, the material forthermal casing 64 for the portion of the thermal well immersed in thethermal pool can be constructed from a material such as the grout usedin the SWEGS prior art system.

Likewise, in some embodiments of the invention, more complex physicalstructures can be created in the Heat Absorption Zone, such as a networkof drilled passageways to facilitate thermal migration. Also, a fluid,such as a glycol based fluid or a molten salt, can also be placed in thebottom of the thermal well, so that the thermal mass is completely orpartially immersed in a bath of hot liquid when in the Heat AbsorptionZone. The detailed designs of these structures created in the HeatAbsorption Zone will, however, vary depending on the details of thegeological strata and local thermal properties in the thermal well.

Although the descriptions presented here typically describe the use of asingle thermal mass on a given suspension cable, another embodiment ofthe invention can have multiple thermal masses on a suspension system ortrack. Also, although the well shafts in this disclosure have typicallybeen illustrated as vertical shafts into the ground, alternative, angledwell shafts could also be employed, especially if a track were to beinserted into the well shaft to allow a “train” of thermal masses to beinserted into a Heat Absorption Zone. Such a thermal “train” may atfirst seem awkward because of its additional weight, but if anembodiment of the invention using a pair of “trains” arranged using twoshafts in a counterbalance arrangement were employed, the energyacquired by one “train” as it was pulled into the Earth by gravity wouldbalance the energy needed to pull the second “train” out of itsrespective well shaft, with the only significant losses due to frictionof the “train” with its track and the friction of the moving cables, andthe drag caused by the rush of the wind flowing past the thermal“train”.

A Molten Salt Closed Loop Embodiment of the Invention

In the previously described embodiments, a thermal fluid such as moltensalt is placed in cavity within a thermal mass. The heat is acquired ina Heat Absorption Zone, and then transferred to a thermal reservoir inthe Heat Transfer Zone.

Variations of another embodiment of the invention using a thermalmaterial such as molten salt without bundling the thermal material in athermal mass are illustrated in FIG. 19 and FIG. 20. In this embodiment,the thermal material does not need to be liquid at the beginning of thecycle, and can in some embodiments be a solid, such as ground orpowdered solid salt at room temperature. In a facility 5012 built at ornear the surface of the Earth 10, a circulating system 5018 directs thismaterial into a first well shaft 5014, which can comprise a drivingapparatus such as a screw 5050, as illustrated in FIG. 19, or apneumatic conveyor system installed in all or part of the well shaft5014, or, as illustrated in FIG. 20, can simply be empty.

This driving apparatus can fill the well shaft 5014, or be in severalstages at various depths. In some embodiments of the invention maycomprise an additional driver 5100 such as a ram screw that drives thethermal material into a chamber 5080 formed in the Heat Absorption Zonesituated in the thermal pool 560.

As the thermal material progresses into the Earth to the Heat AbsorptionZone, it heats up and, if it is a material such as a solid salt mixture,it will melt and become a liquid at higher temperatures. This meltedmaterial 5055 fills or partially fills the thermal chamber 5080, whereit continues to absorb heat.

The pressure in the chamber 5080 created by the force on the thermalmaterial provided by the additional driver 5100 pushes the hot material5055 into the exit pipe 5040, where it proceeds to rise again throughthe exit pipe 5040 in a second well shaft 5016 to the surface of theEarth 10 and from there into the Heat Transfer Zone in a productionfacility 5020.

The exit pipe 5040 can surrounded by insulation 5062 for all or part ofits length, and be designed as shown in the FIG. 19 and FIG. 20 withdecreasing diameters for the cooler sections near the surface of theEarth 10. With the same inflow of material at the base of the exit pipe5040, the thermal fluid in the sections of the exit pipe 5040 having asmaller diameter will have correspondingly higher velocity, andtherefore have less time to cool as it rises to the Heat Transfer Zone.

Once in the Heat Transfer Zone, heat transfer from the thermal materialproceeds as in the previously described embodiments. However, in thisembodiment, the thermal materials can be cooled all the way down to roomtemperature, since the material does not need to be in liquid form forre-injection into the first well 5014. If the thermal material is, forexample, molten salt, the additional temperature change from its meltingpoint (142° C.) to room temperature (20° C.) can, using the numbers fromTable I, represent an additional transfer of 190 kJ of heat per kilogramof material.

As disclosed in the previous embodiments, the well heads and surfacecirculating system 5018 can be enclosed in a facility 5012 which can beconnected to or otherwise integrated with the production facility 5020.

With this application, several embodiments of the invention, includingthe best mode contemplated by the inventors, have been disclosed. Itwill be recognized that, while specific embodiments may be presented,elements discussed in detail only for some embodiments may also beapplied to others.

It will also be recognized that, while generating electricity is acommon end use for the heat produced by these embodiments in the HeatTransfer Zone, other industrial processes, such as electrolysis of waterfor the generation of hydrogen and oxygen; or such as pyrolysis oforganic materials for the generation of “Syngas” or for wasteprocessing; or the direct generation of mechanical energy using a steamturbine; or for the heating of objects for industrial smelting, baking,or curing processes, may all be driven by the geothermal heat harvestedaccording to the invention. It will also be recognized that the thermalmass can comprise additional chambers and constructions designed tofacilitate some or all of the steps of these industrial processes whilethe thermal mass is still present into the Heat Absorption Zone. Otherprocesses and end uses for the geothermal heat that may be known tothose skilled in the art.

While specific materials, designs, configurations and fabrication stepshave been set forth to describe this invention and the preferredembodiments, such descriptions are not intended to be limiting.Modifications and changes may be apparent to those skilled in the art,and it is intended that this invention be limited only by the scope ofthe appended claims.

What is claimed is:
 1. A method for transferring geothermal heat,comprising the steps of: preparing a thermal mass; lowering the thermalmass to a heat absorption zone; raising the thermal mass to a heattransfer zone; and transferring the heat out of the thermal mass.
 2. Themethod of claim 1, in which the step of preparing the thermal masscomprises attaching the thermal mass to a suspension cable.
 3. Themethod of claim 1, in which the step of transferring the heat out of thethermal mass comprises transferring the thermal mass to a thermalreservoir.
 4. The method of claim 1, in which the thermal mass comprisesa chamber for containing a thermal fluid; and the step of transferringthe heat out of the thermal mass comprises transferring the thermalfluid contained in the thermal mass out of the thermal mass.
 5. Themethod of claim 4, in which the step of transferring the heat out of thethermal mass additionally comprises transferring the thermal fluid intoa thermal reservoir.
 6. The method of claim 4, in which the Thermalfluid comprises water.
 7. The method of claim 4, in which the thermalfluid comprises a molten salt.
 8. The method of claim 7, in which themolten salt comprises potassium calcium nitrate.
 9. The method of claim7, in which the molten salt comprises potassium nitrate.
 10. The methodof claim 7, in which the molten salt comprises sodium fluoride.
 11. Themethod of claim 1, in which the thermal mass comprises a heat exchanger;and the step of transferring the heat out of the thermal mass comprisespassing a transfer fluid through the heat exchanger.
 12. The method ofclaim 11, in which the step of transferring the heat out of the thermalmass additionally comprises storing the transfer fluid that has passedthrough the heat exchanger in a thermal reservoir.
 13. The method ofclaim 12, in which the transfer fluid is transferred into the thermalmass from a cool reservoir.
 14. The method of claim 11, in which thetransfer fluid passing through the heat exchanger of the thermal massalso passes through a second heat exchanger in the heat transfer zone.15. The method of claim 11, in which the transfer fluid comprises water.16. The method of claim 11, in which the transfer fluid comprises aglycol-based fluid.
 17. The method of claim 11, in which the transferfluid comprises a molten salt.
 18. The method of claim 17, in which themolten salt comprises potassium calcium nitrate.
 19. The method of claim17, in which the molten salt comprises potassium nitrate.
 20. The methodof claim 17, in which the molten salt comprises sodium fluoride.
 21. Themethod of claim 3, 5 or 12 in which the heat transferred to the thermalreservoir is used to generate electricity.
 22. A thermal mass,comprising an internal chamber at least partially filled with a thermalfluid and in which the remainder of the chamber is filled with a covergas; a first connector to enable the insertion of the thermal fluid intothe thermal mass; and a second connector to enable the removal of thethermal fluid from the thermal mass.
 23. The thermal mass of claim 22,in which the thermal fluid comprises water.
 24. The thermal mass ofclaim 22, in which the thermal fluid comprises a molten salt.
 25. Thethermal mass of claim 24, in which the molten salt comprises potassiumcalcium nitrate.
 26. The thermal mass of claim 24, in which the moltensalt comprises potassium nitrate.
 27. The thermal mass of claim 24, inwhich the molten salt comprises sodium fluoride.
 28. A thermal mass,comprising a internal channel to allow a thermal transfer fluid to flowthrough the thermal mass; and a first connector to enable the insertionof the thermal transfer fluid into the thermal mass; and a secondconnector to enable the removal of the thermal transfer fluid out of thethermal mass.
 29. The thermal mass of claim 28, in which a portion ofthe internal channel has the shape of helix.
 30. The thermal mass ofclaim 28, in which a portion of the internal channel has the shape ofdouble helix.
 31. The thermal mass of claim 28, additionally comprisingan internal chamber at least partially filled with a thermal fluid; andin which at least a portion of the internal channel is surrounded by thethermal fluid.
 32. The thermal mass of claim 31, in which the thermalfluid comprises a molten salt.
 33. A method for transferring geothermalheat, comprising the steps of: preparing at least two thermal massesconnected by a cable; lowering the first thermal mass to a first heatabsorption zone; raising the first thermal mass to a first heat transferzone while simultaneously lowering the second mass to a second heatabsorption zone; transferring the heat out of the first thermal mass;raising the second thermal mass to a second heat transfer zone whilesimultaneously lowering the first mass to the first heat absorptionzone; and transferring the heat out of the second thermal mass.
 34. Themethod of claim 33, in which the steps transferring the heat out of athermal mass comprise transferring the thermal mass to a thermalreservoir.
 35. The method of claim 33, in which at least one of thethermal masses comprises a chamber for containing a thermal fluid; andthe step transferring the heat out of the at least one thermal mass witha chamber comprises transferring the thermal fluid contained in the atleast one thermal mass out of the at least one thermal mass.
 36. Themethod of claim 35, in which the step of transferring the heat out ofthe thermal mass additionally comprises transferring the thermal fluidinto a thermal reservoir.
 37. The method of claim 35, in which thethermal fluid comprises water.
 38. The method of claim 35, in which thethermal fluid comprises a molten salt.
 39. The method of claim 38, inwhich the molten salt comprises potassium calcium nitrate.
 40. Themethod of claim 38, in which the molten salt comprises potassiumnitrate.
 41. The method of claim 38, in which the molten salt comprisessodium fluoride.
 42. The method of claim 33, in which at least one ofthe thermal masses comprises a heat exchanger; and the step oftransferring the heat out of the at least one thermal mass comprisespassing a transfer fluid through the heat exchanger.
 43. The method ofclaim 42, in which the step of transferring the heat out of the at leastone thermal mass with a heat exchanger additionally comprises storingthe transfer fluid that has passed through the heat exchanger in athermal reservoir.
 44. The method of claim 43, in which the transferfluid is transferred into the thermal mass from a cool reservoir. 45.The method of claim 42, in which the transfer fluid passing through theheat exchanger of the thermal mass also passes through a second heatexchanger in the heat transfer zone.
 46. The method of claim 42, inwhich the transfer fluid comprises water.
 47. The method of claim 42, inwhich the transfer fluid comprises a glycol-based fluid.
 48. The methodof claim 42, in which the transfer fluid comprises a molten salt. 49.The method of claim 48, in which the molten salt comprises potassiumcalcium nitrate.
 50. The method of claim 48, in which the molten saltcomprises potassium nitrate.
 51. The method of claim 48, in which themolten salt comprises Sodium fluoride.
 52. The method of claim 34, 36 or43 in which the heat transferred to the thermal reservoir is used togenerate electricity.
 53. The method of claim 33, in which the firstheat absorption zone and the second heat absorption zone are both inapproximately the same location; and the first heat transfer zone andthe second heat transfer zone are both in approximately the samelocation.
 54. The method of claim 53, in which the first heat absorptionzone and the second heat absorption zone are both at the bottom of awell shaft; and the first heat transfer zone and the second heattransfer zone are both near the top of the well shaft.
 55. A method forextracting geothermal energy from the Earth, comprising the steps of:lowering a quantity of salt into a geothermal heat absorption zone;heating the quantity of salt; raising the quantity of salt to a heattransfer zone; and transferring the quantity of salt into a thermalreservoir.
 56. The method of claim 55, in which the quantity of salt isinitially in solid form, and in which heating the quantity of saltcomprises melting the salt.
 57. The method of claim 56, in which thesolid form of the salt is a powder.
 58. The method of claim 55, in whichthe step of lowering a quantity of salt comprises moving the quantity ofsalt with a screw mechanism.
 59. A method for generating electricity,comprising the steps of: heating a thermal mass in a heat absorptionzone; raising the thermal mass to a heat transfer zone; transferring theheat out of the thermal mass and into a thermal reservoir; using theheat in the thermal reservoir to drive a turbine that generateselectricity.
 60. A method for generating electricity, comprising thesteps of: lowering a quantity of salt into a geothermal heat absorptionzone; heating the quantity of salt; raising the quantity of salt to aheat transfer zone; transferring the quantity of salt into a thermalreservoir using the heat from the salt in the thermal reservoir to drivea turbine that generates electricity.